Oftentimes, a trailer hitch is a removable hitch and is held in place on a vehicle with a hitch pin. Such hitch pins typically have either a handle on one end that is larger than the apertures of the removable hitch or a bend in the shaft to prevent the pin from sliding through the apertures, and a cotter key (also called a cotter pin) or similar locking mechanism disposed through the other end for holding the pin in place during transport. This is designed to prevent the pin from being jostled out of place during transport which would allow the trailer to come free from the vehicle.
Cotter keys are often very difficult to remove from the hitch pin, which encourages many people to disregard them and use the hitch pin with no locking mechanism to secure it in place. This is very dangerous because trailers often shift and bounce a great deal during transport, and the likelihood of losing or displacing the hitch pin becomes increasingly high as the distance traveled increases.